Nature-Inspired Glycosylation Strategy Enabled Hydrosoluble Polyhydric Thioalkylated Ferrocene Derivatives for pH-Neutral Aqueous Redox Flow Batteries

Abstract

Organic molecules have been regarded as promising alternatives in aqueous redox flow batteries, with the aim of reducing reliance on mineral resources. Enhancing the solubility and stability of organic species is essential and requires strategic functional group refinement and molecular structure optimization. However, there are relatively few solubilization strategies of naturally water-solubilizing groups in ARFBs. Sugars, i.e., carbohydrates, ubiquitous in nature and indispensable as nutrients, possess an exceptional hydrophilic property and offer a sustainable pathway for molecular functionalization. Herein, we present a thioglucose functionalization strategy to synthesize highly soluble ferrocene derivatives via convenient thioetherification reactions under mild conditions. Under the hydrophilic effect of abundant highly polar hydroxyl moieties, the as-synthesized glycosyl-functionalized thioalkylated ferrocene derivative, namely, Fc-(Thio-Glc)₂, exhibits high water solubility (1.3 M in 1.0 M KCl solution) and favorable electrochemical properties. Molecular dynamics simulations manifest the effects of hydrogen bond networks on the molecular configuration and solvation behavior. Ex situ spectroscopic analyses confirmed the high reversibility and long-term operation stability of Fc(Thio-Glc)₂. Consequently, the pH-neutral ARFBs assembled with the 0.5 M Fc(Thio-Glc)₂ catholyte achieve a capacity retention of 99.995% per cycle or 99.82% per day. This study highlights the tremendous potential of a bioinspired molecular engineering strategy in advancing safe, stable, and sustainable ARFBs toward large-scale energy storage applications.